Dimeric carbonylation of 1,3-alkadiene

ABSTRACT

This invention provides a process for dimeric hydroesterification of 1,3-alkadiene in the presence of a catalyst which is a stabilized complex of palladium, tertiary phosphine ligand and thiol compound.

BACKGROUND OF THE INVENTION

Catalytic carbonylation of olefinic and acetylenic compounds to formoxygenated derivatives with an increased content of carbon atoms is awell-established technology. Various developments and improvements aredescribed in U.S. Pat. Nos. such as 2,768,968; 2,863,911; 2,876,254;3,040,090; 3,455,989; 3,501,518; 3,507,891; 3,652,655; 3,660,439;3,700,706; 3,723,486; 3,746,747; 3,755,419; 3,755;421; 3,793,369;3,856,832; 3,859,319; 3,887,595; 3,906,015; 3,917,677; 3,952,034;3,992,423; 4,102,920; 4,245,115; 4,246,183; and references citedtherein.

Of particular interest with respect to the present invention is thechemical literature relating to dimeric carbonylation of aliphaticconjugated dienes in the presence of a hydroxylated coreactant and acatalyst complex of a Group VIII noble metal and a Group VA tertiarydonor ligand. The dimeric carbonylation reaction is illustrated by thefollowing chemical equation with respect to the interaction of1,3-butadiene with alkanol: ##STR1##

In a report published in Tetrahedron, 28, 3721 (1972), there isdescribed a dimeric carbonylation of 1,3-butadiene in the presence ofalkanol and a palladium-phosphine complex catalyst to yield alkyl3,8-nonadienoate. The publication discloses that the absence of halidecoordinated to the palladium metal is essential for the formation ofalkyl nonadienoate product. In the presence of halide, one mole of1,3-butadiene reacts with one mole of carbon monoxide and one mole ofalkanol to yield alkyl 3-pentenoate.

U.S. Pat. No. 4,124,617 describes a process for the selective productionof fatty acid derivatives from aliphatic diene substrates, in thepresence of dual-function homogeneous palladium complexes and certainclassses of organic tertiary nitrogen bases. One aspect of this type ofprocess is that the use of tertiary nitrogen bases promotes theproduction of various byproducts such as C₅ -esters. Another aspect isthat the catalyst tends to exhibit a reaction rate decrease during thecourse of the carbonylation reaction due to instability of the catalystsystem.

Further, in processes for dimeric carbonylation of aliphatic conjugateddienes such as are disclosed above, the dimeric product is separatedfrom the catalyst complex and other components of the reaction productmixture employing conventional techniques such as distillation. In suchproduct recovery procedures some of the catalyst complex (e.g.,palladium-phosphine complex) is lost by precipitation, and moresignificantly, the catalyst complex invariably suffers from a loss ofreactivity. This is a serious consequence for purposes of a catalystcomplex which is intended to be recovered and recycled in a dimericcarbonylation process. The efficiency of the process is dependent on thestability and reactivity of the catalyst system.

Accordingly, it is a main object of this invention to provide animproved process for conversion of aliphatic conjugated dienes intofatty acid derivatives.

It is another object of this invention to provide a process forproducing alkyl nonadienoate by dimeric carbonylation of 1,3-alkadienewith improved conversion and selectivity.

It is a further object of this invention to provide a stabilizedpalladium catalyst solution adapted for carbonylation of olefinichydrocarbons.

Other objects and advantages of the present invention shall becomeapparent from the accompanying description and illustrative processingdata.

DESCRIPTION OF THE INVENTION

One or more objects of the invention are accomplished by a process fordimeric hydroesterification of 1,3-alkadienewhich comprises (1) reacting1,3-alkadiene with carbon monoxide and alkanol in a liquid mediumcontaining a stabilized halide-free catalyst complex of palladium salt,tertiary phosphine ligand and thiol compound; and (2) recovering dimericalkyl alkadienoate product.

The term "1,3-alkadiene" is meant to include acyclic 1,3-diene compoundswhich contain between about 4-12 carbon atoms, and which can containother heteroatoms such as oxygen, sulfur, nitrogen and halogen which donot interfere with the invention process carbonylation. Illustrative ofsuitable 1,3-alkadiene compounds are 1,3-butadiene;2-methyl-1,3-butadiene; 2,3-dimethyl-1,3-butadiene;2-chloro-1,3-butadiene; 1,3-pentadiene; 5-phenyl-1,3-pentadiene;1,3-hexadiene; 1,3-decadiene; and the like.

The present invention process is particularly adapted for converting alinear 1,3-alkadiene into a dimeric hydroesterification product with ahigh selectivity ratio of straight chain to branched chain product(e.g., a ratio of at least 9:1).

Further, under optimal conditions 1,3-butadiene is at least 80 percentconverted, and the selectivity to alkyl nonadienoate product is at least80 mole percent, based on the total moles of conversion products.

The term "alkanol" is meant to include primary, secondary and tertiaryaliphatic alcohols which are suitably reactive under the carbonylationconditions. The alkanol reactant can be employed in essentially anyproportion as dictated by practical considerations, e.g., at least about0.5 moles of alkanol per mole of 1,3-alkadiene charged. A large excessof alkanol (e.g., up to about 10 moles per mole of 1,3-alkadiene) isemployed if the alkanol is to function also as a solvent medium.

Illustrative of suitable alkanols are primary, secondary and tertiaryalkanol reactants containing between about 1-12 carbon atoms and betweenabout 1-4 hydroxyl groups, such as methanol, ethanol, 2-chloroethanol,2-propanol, t-butanol, pentanol, cyclohexanol, decanol, dodecanol,ethyleneglycol, glycerine, 1,4-butanediol, pentaerythritol,trimethanolpropane, and the like.

It is preferred that the carbon monoxide is introduced into the processreaction system up to a partial pressure of between about 100 and 2000psi of carbon monoxide. The carbon monoxide environment in the processsystem can contain one or more inert gases such as nitrogen, helium,argon, and the like. For optimal results it is essential that theprocess is conducted in a deoxygenated environment, so as not to affectadversely the 1,3-alkadiene conversion rate and the selective yield ofalkyl nonadienoate product.

The liquid medium in the first step of the process can include a solventdiluent, in addition to the other liquid constituents in thecarbonylation reaction system. Suitable solvents include propane,butane, pentane, cyclopentane, hexane, cyclohexane, heptane, octane,tetradecane, petroleum refinery light hydrocarbon mixtures, benzene,chlorobenzene, nitrobenzene, toluene, xylene, mesitylene,tetrahydrofuran, dimethylformamide, methyl ethyl ketone, product ester,and the like.

An important aspect of the present invention is the provision of astabilized catalyst which is highly selective for dimeric carbonylationof aliphatic conjugated diene compounds. Thus, in a further embodimentthe present invention provides a catalyst composition consisting of asolvent solution of solute components comprising a halide-free complexof palladium salt and tertiary phosphine ligand which is in contact witha stabilizing quantity of thiol compound.

The "solvent" in the said catalyst composition can comprise an inertsolvent diluent of the type previously described, and/or 1,3-alkadiene,and/or alkanol, and/or tertiary phosphine, and the like. The saidcatalyst composition can be performed prior to introduction into acarbonylation reaction zone, or it can be formed in situ by the separateintroduction of the palladium salt, tertiary phosphine ligand and thiolcomponents into the carbonylation reaction zone.

The palladium precursor compound preferably is in the form of apalladium-containing compound such as palladium acetate, palladiumpropionate, palladium acetylacetonate, palladium nitrate, palladiumsulfate, bis-(1,5-diphenyl-3-pentadienone)palladium(o) and the like,with the exclusion of any halide-containing salts such as palladium(II)chloride.

With reference to the tertiary phosphine ligand, the term "phosphine" ismeant to include corresponding phosphite derivatives. Illustrative ofsuitable tertiary phosphine ligands are triisopropylphosphine,tri-n-butylphosphine, triisobutylphosphine, tricyclohexylphosphine,triphenylphosphine, tritolylphosphine, tribenzylphosphine, and thecorresponding phosphite compounds. The substituents in the tertiaryphosphine ligands can be the same or different, and mixtures of tertiaryphosphine ligands can be employed. Illustrative of a ligand mixture isone containing about 70-99 mole percent trialkylphosphine (e.g.,triisopropylphosphine) and about 1-30 mole percent triarylphosphine(e.g., triphenylphosphine). A preferred class of tertiary phosphineligands are trialkylphosphines in which each alkyl group containsbetween 2 and about 8 carbon atoms.

An essential aspect of the present invention catalyst system is theinclusion of a thiol compound in the catalyst composition or in thecarbonylation reaction system in a quantity sufficient to stabilize thecatalyst complex of palladium salt and tertiary phosphine ligand. Thestabilizing agent can be any compound which contains one or more thiolgroups, and which is soluble in the liquid reaction medium in thecarbonylation zone.

A preferred class of thiol compounds is that corresponding to theformula:

    R--SH

where R is an aliphatic, alicyclic or aromatic substituent containingbetween about 1-30 carbon atoms.

Illustrative of suitable thiol compounds are methanethiol, ethanethiol,1,1-dimethylethanethiol, 1-methylpropanethiol, 1-butanethiol,1-tridecanethiol, cyclohexanethiol, benzenethiol, 1,4-butanedithiol, andthe like.

The catalyst complex of palladium salt/tertiary phosphine/thiol compoundis provided in the carbonylation reaction medium in at least a catalyticquantity, and the mole ratio of 1,3-alkadiene to catalyst complexpreferably is at least 25:1.

The palladium and tertiary phosphine ligand in the carbonylation zoneliquid reaction medium typically are provided in a ratio between about1-12 moles of tertiary phosphine ligand per gram atom of palladiummetal.

The palladium and thiol compound in the carbonylation zone liquidreaction medium typically are provided in a ratio between about 1-20moles of thiol compound per gram atom of palladium metal. If a largeexcess of thiol compound is employed, then there is formation of C₅thioloate ester in place of alkanol-derived dimeric hydroesterificationproduct.

It is highly preferred that the dimeric carbonylation step of theinvention process is conducted in the presence of a vinyl polymerizationinhibitor, e.g., hydroquinone. If an inhibitor is not included in thereaction system then there is an increased incremental loss of1,3-alkadiene to polymeric byproducts. When a polymerization inhibitoris employed, the yield of byproducts can be limited to less than about 5percent. The byproducts produced during 1,3-butadiene dimericcarbonylation, for example, include alkyl 3-pentenoate;vinylcyclohexene; 1,3,7-octatriene; 1-methoxy-3,7-octadiene; andoligomeric polyenes.

The temperature for the first step dimeric carbonylation reaction canvary in the range between about 0° and 150° C., and preferably is in therange between about 80° C. and 120° C.

The pressure in the first step reaction zone can vary in the rangebetween about 300 and 2000 psi, and preferably is in the range betweenabout 400 and 750 psi. As previously indicated, it is advantageous toprovide a carbon monoxide partial pressure in the range between about100 and 2000 psi in the first step reaction zone.

In a typical batch type process, the reaction time for the dimericcarbonylation step will average in the range between about 2 and 25hours, as determined by temperature and pressure parameters and thereactivity of the palladium-phosphine-thiol complex catalyst.

After the completion of the first step dimeric carbonylation reaction,the liquid product mixture is cooled to room temperature or lower. Anyhigh molecular weight polyene byproducts in the reaction product mixturetend to precipitate out during the cooling stage. As necessary, thereaction product mixture can be filtered to remove polymericprecipitate.

The product mixture is then fractionated by a conventional method suchas distillation to recover the alkyl alkadienoate product. It is highlyadvantageous to leave some alkyl alkadienoate as a residual solventmedium for the catalyst complex which is in solution. The said solventsolution of catalyst can be recycled to the carbonylation step of theprocess.

In a batch type process, it is convenient and advantageous to performseveral dimeric carbonylation runs successively in the same reactorsystem, without recovery of alkyl alkadienoate product between therespective runs. The accumulated product is recovered after thecompletion of the last run.

In another embodiment, this invention contemplates a continuous processfor producing and recovering alkyl alkadienoate. Illustrative of aspecific application of the continuous process, a solution ofpalladium-phosphine-thiol complex and alkanol is fed continuously to afirst reaction zone of an elongated reactor system, simultaneously withthe introduction of 1,3-butadiene. In the first reaction zone, the feedmaterials are admixed efficiently with each other and with carbonmonoxide which is present at a partial pressure of at least 100 psi(e.g., 400-1000 psi). The admixture is passed into a second reactionzone of the reactor system, in which zone there is no input ofadditional carbon monoxide. The temperature and flow rates arecontrolled in the second reaction zone so that optimal proportions of1,3-butadiene and carbon monoxide are reacted. The presence ofincremental carbon monoxide is maintained in the second reaction zone ina quantity sufficient to prevent the formation of alkoxyoctadienebyproducts, but not sufficient to favor the formation of palladiumpoly-carbonyl and poly-palladium carbonyl complex species.

A product stream is removed continuously from the end of the secondreaction zone. The product stream is distilled to remove a portion ofthe alkyl nonadienoate product. The residual solution of product andcatalyst is recycled to the first reaction zone of the dimerichydroesterification system.

The following examples are further illustrative of the presentinvention. The reactants and other specific ingredients are presented asbeing typical, and various modifications can be devised in view of theforegoing disclosure within the scope of the invention.

EXAMPLE I

This Example illustrates the preparation of a stabilized catalystcomposition.

Into a nitrogen-flushed flask are charged sequentially palladium(II)acetate (0.9 gram, 4.0 mmoles), 20 milliliters of dry deoxygenatedtetrahydrofuran, triisopropylphosphine, (0.7 gram, 4.5×10⁻³ mole) and0.5 gram of hydroquinone. Upon stirring this mixture at room temperaturefor 15 minutes, a deep red-brown solution results. The tetrahydrofuranis removed on a rotary evaporator at <50° C. leaving a red-brown solid,which constitutes a standard catalyst composition in accordance with thepresent invention.

EXAMPLE II

This Example illustrates the dimeric hydroesterification of1,3-butadiene.

A nitrogen-flushed stainless steel cylinder is charged with a standardcatalyst composition (in accordance with Example I), dissolved in 0.46mole of methanol, and with 0.093 mole of 1-butanethiol, 4.0 mmolestriisopropylphosphine, and 0.048 mole of tetradecane (as a g.c. internalstandard).

Into a second cylinder is placed 0.926 mole of 1,3-butadiene. The twocylinders are installed into a reactor system which allows injection ofthese solutions into an autoclave reactor using carbon monoxidepressure.

A 300 milliliter 316 SS magnadrive autoclave is evacuated to 0.1 torr toremove any volatile impurities, flushed with carbon monoxide and thencharged at room temperature with the catalyst solution employing 100psia of carbon monoxide. The 1,3 -butadiene is charged into theautoclave reactor employing 500 psia of carbon monoxide. Reactortemperature is brought to 100° C. as quickly as possible (about one halfhour) and stabilized at this temperature. Reactor pressure is maintainedat 750 psia using carbon monoxide fed from a one liter storage vessel.

The reaction is followed as a function of time by observing both thechange in pressure in the one liter storage vessel and the appearance ofproducts by g.c. A one milliliter sample is taken from a bottom liquidsampling tap on the autoclave at a given time. This sample line iswashed with pentane and flushed with nitrogen after each sample istaken.

After 21 hours of reaction time, a 70 percent 1,3-butadiene conversionis observed with a 48 percent yield of methyl 3,8-nonadienoate (0.224mole). Other conversion products detected are 4-vinylcyclohexene (0.01mole), 3,5,7-octatriene (0.011 mole), cyclooctadiene (0.013 mole),l-butyl 3-thiolopentenoate (0.029 mole), 1-butyl thiolononadienoate(0.03 mole) and methyl 3-pentenoate (0.04 mole). No visible palladiumblack is observed in the reaction system.

EXAMPLE III

The procedure is the same as Example II, except that 5.3 mmoles of1-butanethiol, a 125° C. reaction temperature and a 350 psi reactorpressure are employed.

After 26 hours of reaction time, a 75 percent yield of methyl3.8-nonadienoate (based on initial 1,3-butadiene charged) is produced,at an STY of 219 grams of methyl 3,8-nonadienoate per liter hour (at0-50 percent butadiene conversion). Other products observed are methyl3-pentenoate (0.2 percent), 4-vinylcyclohexene (1.9 percent) and1,5-cyclooctadiene (4.4 percent). No visible palladium black is observedin the reaction system.

What is claimed is:
 1. A process for dimeric hydroesterification of1,3-alkadiene which comprises (1) reacting 1,3-alkadiene with carbonmonoxide and alkanol in a liquid medium containing a stabilizedhalide-free catalyst complex of palladium, tertiary phosphine ligand andthiol compound; and (2) recovering dimeric alkyl alkadienoate product.2. A process in accordance with claim 1 wherein the 1,3-alkadienereactant in step(1) is a normal 1,3-alkadiene containing between about4-12 carbon atoms.
 3. A process in accordance with claim 1 wherein thealkanol reactant in step(1) is a primary, secondary or tertiary alkanolcontaining between about 1-12 carbon atoms and between about 1-4hydroxyl groups.
 4. A process in accordance with claim 1 wherein theliquid medium in step(1) comprises an organic solvent solution ofreactants and catalyst complex.
 5. A process in accordance with claim 1wherein the catalyst complex in step(1) is provided in at least acatalytic quantity, and the mole ratio of 1,3-alkadiene to catalystcomplex is at least 25:1.
 6. A process in accordance with claim 1wherein the palladium and tertiary phosphine ligand in the step(1)liquid medium are in a ratio between about 1-12 moles of tertiaryphosphine ligand per gram atom of palladium metal.
 7. A process inaccordance with claim 1 wherein the palladium and thiol compound in thestep(1) liquid medium are in a ratio between about 1-20 moles of thiolcompound per gram atom of palladium metal.
 8. A process in accordancewith claim 1 wherein the step(1) reaction is conducted at a temperaturebetween about 0°-150° C. for a reaction period between about 2-25 hours.9. A process in accordance with claim 1 wherein the step(1) reaction isconducted at a pressure between about 100-2000 psi.
 10. A process inaccordance with claim 1 wherein the 1,3-alkadiene reactant in step(1) is1,3-butadiene and the recovered product in step(2) is alkyl3,8-nonadienoate.
 11. A process in accordance with claim 1 wherein the1,3-alkadiene reactant in step(1) is a 2-methyl-1,3-butadiene.
 12. Aprocess in accordance with claim 1 wherein the 1,3-alkadiene reactant instep(1) is 1,3-pentadiene.
 13. A process in accordance with claim 1wherein the 1,3-alkadiene reactant in step(1) is 1,3-hexadiene.
 14. Aprocess in accordance with claim 1 wherein the alkanol reactant instep(1) is methanol.
 15. A process in accordance with claim 1 whereinthe alkanol reactant in step(1) is ethanol.
 16. A process in accordancewith claim 1 wherein the alkanol reactant in step(1) is ethyleneglycol.17. A process in accordance with claim 1 wherein the alkanol reactant instep(1) is 1,4-butanediol.
 18. A process in accordance with claim 1wherein the alkanol reactant in step(1) is pentaerythritol.
 19. Aprocess in accordance with claim 1 wherein the alkanol reactant instep(1) is trimethanolpropane.
 20. A process in accordance with claim 1wherein the palladium component in the step(1) catalyst complex ispalladium diacetate.
 21. A process in accordance with claim 1 whereinthe palladium component in the step(1) catalyst complex isbis(1,5-diphenyl-3-pentadienone)palladium(o).
 22. A process inaccordance with claim 1 wherein the tertiary phosphine ligand in thestep(1) catalyst complex is trialkylphosphine.
 23. A process inaccordance with claim 1 wherein the tertiary phosphine ligand in thestep(1) catalyst complex is triisopropylphosphine.
 24. A process inaccordance with claim 1 wherein the tertiary phosphine ligand in thestep(1) catalyst complex is tri-n-butylphosphine.
 25. A process inaccordance with claim 1 wherein the tertiary phosphine ligand in thestep(1) catalyst complex is tri-secondary-butylphosphine.
 26. A processin accordance with claim 1 wherein the thiol compound in the step(1)catalyst complex corresponds to the formula:

    R--SH

where R is an aliphatic, alicyclic or aromatic substituent containingbetween about 1-30 carbon atoms.
 27. A process in accordance with claim1 wherein the thiol compound in the step(1) catalyst complex is1,1-dimethylethanethiol.
 28. A process in accordance with claim 1wherein the thiol compound in the step(1) catalyst complex is1-butanethiol.
 29. A process in accordance with claim 1 wherein thethiol compound in the step(1) catalyst complex is 2-butanethiol.
 30. Aprocess in accordance with claim 1 wherein the thiol compound in thestep(1) catalyst complex is benzenethiol.
 31. A process in accordancewith claim 1 wherein the thiol compound in the step(1) catalyst complexis 1-tridecanethiol.
 32. A process in accordance with claim 1 wherein avinyl polymerization inhibitor is present in the step(1) liquid medium.33. A process in accordance with claim 1 wherein a liquid fractioncontaining stabilized catalyst complex is recovered in step(2) andrecycled to step(1 ).